In the Dutch Wadden Sea, Seals Stay Healthy Avoiding Others

Aerial surveys of the North Sea show that some seals practice social distancing, probably for the same reason that humans do – to keep disease from spreading.  The research appears in the journal Royal Society Open Science.

The scientists peeped in on two species of seal – harbor and gray – on the coast of the Dutch Wadden Sea, where both species hang out on the intertidal flats and beaches to mate, give birth, and rest. They number in the thousands – up to 6,500 gray seals on the high sandbanks, with 8,000 or so harbor seals on the sand flats at low tide.

“By comparing harbor seal colonies with gray seal colonies, we have found that harbor seals keep a greater distance from their neighbors than gray seals do,” the report’s lead author, Jeroen Hoekendijk, of the Royal Netherlands Institute for Sea Research and Wageningen Marine Research, told the Guardian.

One would think that the social-distancing harbor seals are better at avoiding disease than the grays, but that’s not the case. Harbor seals have had disastrous disease outbreaks, such as phocine distemper virus in 1988 and 2002 that wiped out half the population. Gray seals, which are genetically more resistant to respiratory viruses, were relatively unharmed.

The researchers believe that the social distancing they observed is the result of the seals’ memory of those terrible outbreaks. Says Hoekendijk, “The greater inter-animal distances that we’ve observed for harbor seals in our study might be a response … very similar to our response during the Covid pandemic.”

The researchers admit that their findings are far from conclusive: “Although our findings confirm the existence of social distancing in harbor and gray seals, it cannot be concluded whether or not it is an evolutionary response to limit pathogen transmission, because no data was available from before or during these outbreaks.”

Photo credit: Pieter Beens / Royal Netherlands Institute for Sea Research